In many subterranean microbial processes, nutrient selection and injection are controlling factors to successful operations. The microorganisms utilized must be nutritiously sustained and metabolically active and thus able to achieve their specific objective.
Numerous microorganisms suitable for achieving various microbial objectives in subterranean formations are known in the art. In order to achieve a specific microbial objective, suitable microorganisms can be selected and injected into the subterranean formation. Oftentimes, however, endogenous microorganisms well suited for achieving a particular microbial objective are already present within the formation.
Recently, a method was disclosed by Clark, et al. (U.S. Pat. No. 5,083,611 assigned to Phillips Petroleum Company), which overcame many problems associated with microbial nutrient injection methods then known to the art. This newly disclosed method provides for the sequential injection into a subterranean formation of sources of individual nutrient components which are deficient in the subterranean formation so that a complete nutrient medium capable of sustaining substantial microbial activity is formed in the subterranean formation upon injection of the last nutrient source. Each of the nutrient sources is comprised of at least one of the deficient individual nutrient components. Further, each of the nutrient sources, up to and including the next to the last nutrient source injected, is injected in an amount such that at least one individual nutrient component contained therein is retained in the subterranean formation in an amount sufficient for achieving the desired in-situ microbial objective.
The above method prevents the excessive utilization and depletion of nutrient components by microorganisms located in the vicinity of the borehole and also takes advantage of chromatographic retention in order to achieve nutrient media distribution beyond the proximity of the borehole. However, it has been discovered and disclosed by the present application, that in order to achieve biomass production (i.e. microbial growth and/or exopolymer production) to plug high permeability zones within subterranean formations, a sequestering agent when used in the method of U.S. Pat. No. 5,083,611 and in addition to injected nutrients, exhibits greater plugging potential that in the absence of sequestering agents. The ability of the nutrients to be transported in-depth is therefore of great importance. Some problems associated with the use of known inorganic phosphorus sources is their tendency to complex with multivalent cations within the reservoir which results in poor solubility and heightened difficulty in transport distal to the wellbore. Sequestering agents when injected into subterranean formations bind with the multivalent cations there present, thus allowing free transport of the phosphorus nutrient source.
The present invention provides a method whereby injected sequestering agents increase solubility of the phosphate source thereby improving transportability in porous rock and in addition provide a more soluble source of phosphate to the microorganisms which can then be more readily utilized than the insoluble form.
It is therefore an object of this invention to provide a method of increasing the solubility and transportability of an inorganic phosphorus source for use in the state-of-the art nutrient injection for subterranean microbial processes.
These and other objects of the present invention will become apparent upon inspection of the disclosure and the claims herein provided.